Dual fuel variable speed engine control



R. MlLLER 2,781,030

DUAL EUEL VARIABLE." SPEED ENGINE CONTROL 2 Sheets-Sheet 1 Feb. 12, 1957 Filed Feb. 10, 1954 fzwemar Jul vii JZ'z'ZZer 5 Parker 5 (a rte) Feb. 12, 1957 R. MlLLE R 2,781,030

DUAL FUEL VARIABLE SPEEDENGINE CONTROL 7 Filed'Feb. 10, 1954 2 Sheets-Sheet 2 jiwyenzar '1 @g 2 02",??? ('arfer Jz'farneys United tate atent i 'Manufacturing Company, Milwaukee, Wis a corporation of Wisconsin Application February 10, 1954, Serial No. 409,317

8 Claims. (Cl. 123-27) This is a continuation-in-part and an improvement over Serial No. 77,495, filed February 21, 1949, now abandoned.

My invention relates to a method of and apparatus for controlling the operation of a variable speed dual fuel internal combustion engine of the diesel or pressure ignition type. Oil fuel or gas fuel, or both, may be burned in engines of this nature, and my invention has for one object an arrangement whereby the supply of gas may be controlled by the engine governor throughout the entire range of governor movement, but the supply of oil is controlled by the engine governor throughout only half of the range of governor movement. A constant quantity of pilot oil is supplied during the other half of the range of governor movement as the load varies.

Such an engine is supplied with air under pressure for scavenging and combustion, and any suitable scavenging blower or the like may be used for this purpose. The engine with which my invention is intended to be used or applied is one in which the engine itself supplies'its own air. In other Words, the engine drives a scavenging purnp or blower or the exhaust gases drive a turboblower, and the quantity and pressure of the air vary with the speed and load on the engine.

The governor can be manually set to control or govern the engine at any desired speed, and the'speed setting can be changed by the operator. Once the speed has trated as a separate head for each cylinder though a cylinder head for a multiplicity of cylinders might be used. 3 is an intake valve, and 4 an exhaust valve, and 5 a gas valve, all associated with the single cylinder head. All three of these valves are actuated by rocker arms 6 and 7 rotating onthe rock-er shaft 8 in a bracket 9 on the cylinder head. .The arm 6 actuating the intake valve is omitted for clearness, and the injection nozzle for oil is omitted from this view though of course it will be understood that it Willbe present in a working cylinder head.

10 is a governor and 11 a cam shaft, both of them being driven from the engine crank shaft in any suitable manner not here illustrated. 12 is the exhaust cam, 13 the gas valve cam and 14 the intake valve cam, all three of them on the cam shaft 11. having cam rollers 18 at their lower ends are actuated respectively by the cams 12, 13 and 14 to actuate the exhaust valve 4, the gas valve 5 and the intake valve 3. 19 is a guide link, there being one associated with each of the cam rollers 18. 24 is the oil injection cam on the cam shaft 11. It is engaged by a roller 21, the position of which may be adjusted by means of the worm and gear assembly 22 to vary the operation of the oil injection pump 23 which, through a conduit 24, supplies oil for combustion under pressure to the injection nozzle in the cylinder head.

The details of the exhaust passages and scavenging air manifold associated with the cylinder head are omitted been selected and set by the operator, the governor moves to control the fuel supply to maintain the engine speed within very narrow limits as the load varies.

An object of my invention is a dual fuel internal combustion engine of the combustion ignition type having a gas operating range and an oil operating range.

The gas operating range is on the higher load side of amounts of fuel are supplied to the engine in accordance with the load. During the gas operating range, the

amount of gas fuel being supplied is varied and a quan- H tity of pilot oil is also supplied. During the oil operating range, the amount of oil fuel being supplied is varied. In addition, the pressure of the gas fuel supplied to the engine is varied in accordance with the speed of the engine.

My invention is illustrated more or less diagrammati-Q cally in the accompanying drawings, in which: 7

Figure 1 is an isometric view of the outside ofan engine with the elements of my invention associated therewith; and

Figure 2 is a View similar to Figure 1 showing a modified form of my invention.

An engine block of the usual type is indicated at 1.

It has a removable cylinder head 2, in this case illus-- except that the manifold is shown schematically at 102 with the usual scavenging blower at 194 and a connection 1% leading to the inlet valve 3 for each cylinder, the blower. being driven from the engine by any suitable drive connection. 27 is a gas supply pipe which supplies gas under'pressure for combustion, to the gas manifold 23, the manifold supplying gas to each cylinder head through conduits 29., In normal engine operation it is essential that the pressure in the gas manifold be somewhat higher than the pressure of the scavenging air.

30 is the fuel gas control shaft, 31 the speed control shaft, 32 the fuel oil control shaft, all rotatably mounted in suitable brackets on the engine. A lever 32' which, by a link 33, is connected to a lever 34 on the gas regulating valve housing 35 is keyed to the gas control shaft. The effective length of this link 33 may be adjusted to change thev response of the gas control valve in the housing35 to the angular movement of the gas control shaft 30.

At the outboard end of the gas control shaft 30 is a pointer 37, which travels over an indicator dial 38, the purpose of which will, hereinafter appear. The gas control shaft 30 is actuated by the lever 39, link 40, lever 41 and link 42 from the plate-cam 43 on the governor shaft 44, the, governor shaft, of course, rotating in acadjusted and set by meansof the hand wheel 56 so that the engine speed, controlled by the governor, may be adjusted, the governor being set by the operator for any desired speed.

The fuel oil control governor plate-cam 43 through the rock lever 57, having a cam roller 58 engaging the plate cam. The. cam is in part cylindricalso that within that part of itsrotation called the gas operating range the roller does not move I Patented Feb. 12, 1957 Push rods 15, 16 and 17 Shaft 32 is controlled by the 3 radially and thus there is no change in the angularposition of the shaft 32 within this gas operating range, this being half of the governor plate-cam movement. In the other half of itsfmove'ment, when the plate-cam has rotated" in a clockwise direction into the oii operatingrange, movement of the plate-cam causes'angular movementf the lever 57 and so afiects the fuel'oil 'control shaft 32. The lever'57 is connected by a link 59-and lever 69 to the'fue'l oil control shaft 32, and the shaft 32 is connectcd'by link and lever combination l tofthe pump lito varwin the usual wafig the pump output whereby the speed and load of the engineis controlled underoil governingconditiom-so that when the governor moves through its governor travel, it affects only, the gas, because 'duringtne time that-theplate-cam 'is inits upper positionfits movement control the gas control shaft fstl and has no efiecton the fuel oil control shaft 7 32: Whereas, when the cafnhas moved further in "a clockwise direction to the oil operating range, then movement of the cam controls both the fuel oil control shaft and the gas control shaft. 7

In Figure 1,70 is a manual gas control valve provided with adial so that the operator may set the desired amount of gas entering the gas manifold. 71 is a gas shut-0d valve connected by levers and linkage, through the linkage and lever 73 to the control lever 74, and pivoted on the fuel oil control shaft 32 through a claw 'coupling. 75 is a limit switch adapted to be actuated by a finger 76 on the shaft 32 to control any suitable alarm, if desired.

An operating engine would, of course, have a number of safety mechanisms by which the engine would close down au'tomatically in case of fuel failure, and by which the gas and oil controls are interlocked so that the engine cannot be started,v or rather, an effort cannot'successfully be made to. start it, when something .is out of'order; These form no present part of my invention and are, therefore, not illustrated or discussed. One, purpose of the adjustment 22, by which the leadofthe cam controllingthe pump is: controlled, is to enable the engine to be' specially 'adjusted'for only oil fuel operation.

It will b'elunderstood that with the parts as indicated, the engine is started by first rotating the lever 74 to move the fuel'oilcontrol shaft 32 into startingposition; then when the engine is turned over by any suitable starting f "means, air and oil are supplied. to theengine as it picks a up speed, Then thelever74 is further rotatedinto the 7 r 4 charged air forscavenging, for maximum efiiciency of operation, will be set and determined and marked on the dial 38 for, for instance, 300 revolutions per minute. Under these circumstances, the engine may operate throughout a reasonable speed variation under change in load, the governor controlling: it, so that the control travelwithout in any way affecting the oil.

' ator must again make the manual adjustment of valve .7 70' until, at the desired speed, the pointer 37 returns to the indicatedmaximum point 130' on the dial 38, at

If the. operator nowwants to run the engine at lower speed, he can do so by. adjusting the speed controlled by the governor, but when he does this, he decreases relationship between gas pressure and the reduced scav- 7 enging pressure resulting from the lower speed, the operwhich time speed variation is properly controllable by the governor and a maximum proportion of governor movement remains available.

In thercase of the indicator pointer on the gas regulatingshaft, there is on the dial a point which indicates" approximately 90% opening of the gas valves. This means that whenthe speed or load is' changed to a new condition, by manipulating 'the manual'valve 70, full ln Figure 2, I have shown a modification of Figure 1. A gas throttling or regulating valve is shown in the gas inlet pipe 27. The hand wheel mechanism 54', connectedto the governor forvarying thespeedof the engine, is connected to the valve 76"through an' extended lever 53' and ajlink, this lever being mounted on the speed control shaft BYinamanner' similar to Figure 1. 'A gas shut-ofi-valve 71 is positioned above the regulating valve 7%) and is controlled, as before, by the manually operable lmk-age mechanism 72'. The other details of mecha-' nism and structureand the broad operating principles are the same as before.

running position, the gas supply is manuallyadjusted by valve 70, the valve 7 1'beingnow opened, and the engine will then run with the cam 43in the position shown, r so that, the.governormovement'of the plate-cam 43 'affects' only the gassupply. The. oil is independent of governor movement, because .the oil-lever cam roller '58 engages the cylindrical part of the plate-cam 43 and cam m'ove ment has no effect. If, however, the, load should inr' crease to apoint Where the gas was unable torcarr y the load,v as might-be the case if the gas 'supply'fell off or;

gas pressure reduced, then the engine speed would reduce,

In.-.this modification, when the operator changes the will' vary'directly in accordance with the speed. course, a suitable-adjustment could be provided in the linkage mechanism shown between thevalve 70 and 1ever 53 in Figure 2 'as it is desirable that the pressure of gas beinl 'supplied to the engine always be at'least slightlyf greater thanthe pressure of the scavenging air.

[illustrated a practical and-operative device, nevertheless,

slightly so that the cam 22 controlled by the governor 1 would rotate in a clockwise direction, bringing fthevca'rnj roller 58 into engagement with'thefdiminshed portion of the plate cam.43under ;which circumstancethe fuel con 7 trolfshaft 32 would be rotated to increase the pump output frornthe pilot amount of oil to an-operatingvalue. This;

- situationwouldcontinue, ah increased. amount of, oil beingv :fed. to the engine, as long as theload'remained'suchjw that the roller 58, was on that diminished partlof the cami which calls for oil operation.

When assembled, the engine will sired speed whichdetermines the pressure of ,the. scaiveng; V

ing, then the. amountj of' 'gas'will be adjustedj so. as

tojproduce maximum efiiciency at the obtainedscaveng ing air pressure for maximum load. Thepoint at. which,

the gasadjustment balances properly with the supersure of the air varies with many chan-ges may be madexin the size, shape, arrange ment, number and dis'position of parts 'withoutudeparting materially from; the "spirit of my invention] 1 wish,

therefore, that: my showing be taken as in a large sense illustrative or diagrammatic. ratherthan as'lirniting 'rne 'toimy precise showing Theuse and operation of my invention arelas follows:

My; engine isflsupplied with air nnder 'pre'ssurei for scavenging and combustion, and any suitablerneans maybEJlSEd to provide this air.. Theengine to .whichmy invention is intended to be applied is one wherein the en- "igineitself, either byexhaust turbmbflower or pumpor thelike suppliesitsownair, and so the amountand pres-cs the "speed of land load carried;

byptlie engine,

Such engines are, under normal operating,conditions} supplied with fuel gas. which. whemmixediwith the air doesmot ignite ,reliablyiuncler 'compressionj To; overcome this difiiculty, such an engine is supplied with a minimum amount of pilot fuel oil which ignites easily under compression and inaugurates the burning of the gas-oil mixture.

Gas is a cheaper fuel than oil under many circumstances, and so the less oil burned, the better. However, occasion will occur where the engine must run on oil or must run on gas and more than the amount of pilot oil.

The engine is controlled, as is usual with diesel engines of this type, by a governor 10, and when the engine runs on gas the governor controls the gas in consonance with variation in load to maintain the engine speed in the selected speed range. The pilot oil is not governed, the

engine burns just enough pilot oil on every cycle to in augurate combustion of the gas, and the amount of pilot oil does not usually vary with load or speed.

When the engine is burning oil alone, the oil supply must be governed to compensate for change in load, and if oil and gas are burned, that is more oil than the mere pilot amount, then the governor controls the oil and the gas in consonance to maintain the governed speed.

The governor can be manually set to control or govern the engine at any desired speed and such setting can be changed at the will of the operator. As load varies, the governor moves to control the fuel supply to maintain the engine speed within very narrow limits.

In my herein disclosed arrangement, the gas supply is controlled by the governor throughout the entire range of governor movement but the oil supply is controlled by the governor throughout only one-half of its range of movement. The pilot oil, which does not vary in amount with variation in load, is supplied during the remainder or other half of the range of governor movement With-.

out governor control.

That part'of governor movement during which oil is controlled is called the oil operation range and that part of governor movement during which the oil is not controlled is called the gas operation range. Within the gals operation range, only pilot oil is burned, and the engine is so adjusted that the gas operation range is on the higher load side of the governor movement within the selected load range and only if the load increases to a point such that gas with pilot oil is insufiicient to maintain the speed and carry the load does the governor go down into the oil operation range, in which range if gas is still supplied the engine burns both oil and gas or if gas is shut off the engine burns only oil.

Increase in load, therefore, beyond the limit of the gas operation range causes the governor to move into the oil operation range and this causes an increase of oil supply above the pilot amount and causes the governor to resume control of the oil supply. The engine then burns both gas and a substantial amount of oil, enough over and above the pilot amount to aid the engine to carry the additional load.

It is important that the gas pressure be slightly greater;

than the scavenging air pressure and there is an optimum relationship between these pressures. The gas pressure in the supply main is normally much higher Lhan the pressure desired at the engine, and so pressure reducing means are used. Manual control means are provided between the pressure reducer and the engine to per mit accurate gas pressure control.

The gas supplied to the system from any suitable outside source is normally maintained at constant pressure. The operator may, by setting the manual control valve 7%, adjust the pressure of the gas as it starts toward the engine at any desired point below or susbtantially up to the'pressure at which the gas reaches the system and that manual adjustment is independent of engine operating variations. In that respect, such adjustment is unlike the scavenging air pressure which does not vary in consonance with engine operating variations. And so to insure a satisfactory engine operation, the gas pressure is manually adjusted to insure a proper relation to the scavenging air ent to upset this equilibrium once it has been established,

An indicator will show the position of the gas governing means controlled by the governor for optimum airgas pressure relationship in the desired speed range. This may take the form of a pointer on the gas control shaft and a dial with means for marking on the dial the point at which optimum conditions prevail.

The engine will be so operated, so adjusted, thatthis optimum position will be located approximately at the half-way point in governor movement between the gas operation range and the air operation range, and as load and speed vary, the governor will move back and'forth between this median point and the other end of the gas operation range. If for any reason, such as a decrease in the gas supply or an excessive increase in load, gas is not able to carry theload, the speed will fall slightly and the governor will move down into the oil operation range, perhaps further increasing gas supply, but more important, increasing the amount of oil above the pilot amount to enable the engine to carry the load.

This engine and the control lends itself well to use, for instance, on an oil pipe line where slight changes in speed are of little consequence and also to a situation where it frequently may happen that the operator desires to operate the engine at a speed substantially below the maximum speed for whichthe engine was designed.

If without further change we try to'operate an engine which will run between and 300 revolutions, the governor might control the engine between 150 revolu tions, its low speed, and 300, itshigh speed. if, for example, the engine is to operate ata lower speed and the governor is set to run, for example, at 250 revolutions, the governor never gets up to 300 revolutions because of the governor setting. ;The differential between the gas and air pressures is now a new value, the low speed resulting in a substantially reduced air pressure. This is compensated for by reducing the gas pressure manually so as to return to the original differential between gas and air pressure. In other words, with the engine running at 250, the gas pressure is decreased until the indicator has returned to the optimum point it occupied when the engine was set for 300 revolutions. The governor now is able to move within the original range at the lower speed and the governor will control speed throughout the entire gas operating range and will be able to control the gas supply throughout the entire gas operating range and the oil supply throughout the entire oil operating range just as before, In other words, by this adjustment of gas pressure, I have in eliect increased the range through which the governor operates at any one speed and have avoided the reduction in governor travel or amplitude of operation which normally results from a decrease in speed.

For instance, in the case of a pipeline engine pump combination, an engine might be designed to run at 300 revolutions per minute, at a certain torque. Perhaps the operator wants to run it at 150 revolutions. As above discussed, by manipulating the gas supply and the differential between gas and air, he is able to have the engine run under control of the governor throughout the entire governor range for the gas operated part of the governor movement. while maintaining constant speed at this lower speed, he still may do that because all'he has to do is to continue his manipulation of gas pressure so as to maintain the indicator at the index point determinedin the first instance, at the desired speed and torque, when the engine was set up and operated at maximum speed and maximum relationship between the governor and engine operation 1 If, now, he wants to decrease the torque movement throughout its entire range controls the gas L travel where the change-over from governor control of 79 is changed, the pressure of the gas supplied tothe engine is automatically: varied." Eve.nthough. I" have:

7 shown the linkage mechanism{or-effectingthis-automatic 7 gas pressure variation in speedinFigurdZ as-airigid'link age, it should be understood that any jsuitable' adjustmechanism as shownis schematically 'intendedto repre sent this particular. operating condition; V

- governor with a opcrating r'ange 'and' an oil operating range'i'n the event or" a substantial gas pressure failure; a gas'supply line for supplying gas fuel to the engine V 'fronra gas fuel source, a pump forsupplying oil fuel to the engiue 'from an oil' fucl' sourcepa gas fuel control 1 amount of gas fuel,being'suppliedto-thef enginearraccord anccwith the loadluring-thegas-"operatingrange; anion: 1 fuel control mechanism associated yvjth the governor for' r must be established and maintained such vthat the governor 7 will be able to control the engine speed accurately within its operating range. By my invention 1 havecutthe governor range in half so that half of it controls all operation and half of it controls gas operation, and at 5 the maximum speed and torque I am still able to get" adequate governor control. But a difticulty'arises when speed'or torque are reduced below the maximum because, a under ordinary circumstances, only a part of the'remaining part of the governor movement is available'to efiect control gas. By manipulation ofthe relationship between; 7 gas pressure and scavenging pressure, We are able,;-by manual adjustment, to bring the governor back into a range Where all the availablegovernor travel'is' effectiveto control the speed of the engine. V V 0 Speed droop is not importanton an engine of this sort. The governor 10 may well beset at which" is known as Zero speed droop and the engine will be controlled by the two-stage plate-cam 43 Which controls the oil' supply. f

. Half of the cam' is generallycylindrical and of such radius that a lever supported roller 58 engaging it will hold the oil controls in such positionas to cause the injection of pilot oil only. When the governor drops from the gas operating range to the oil operating range, the roller 58 engages a part of the cam, the radius of which changes, so that as cam movement continues, the fuel'oil control shaft 32 controlling the pump 23 rotates to increase pump displacement so that substantial quantities of fuel oil will be supplied, V r N 9 p This is all done without any change in thegovernor con; 1

V trolled relationship betweenthe engine'and the gas supply,

because the gasrvalve'is controlled by theshaftwhjch is directly connected'to the. governor so that governor valve 35, and so, the gas supply. aThus -in 'one part of the governor movement gas only is governor controlled, and in another part of the governortravelboth gas and e 7 oil are governor controlled. By manipulation of the gas 7 pressure at'any selected speed, the pointin governor;

gas alone to governor control of both gasand oil occurs may always be kept at the center of governor travelso that maximum governor availability and accuracy may be' had at all speeds. j r The operation of the modificationshown in Figure 2 is substantially the same, except that when the operator varies the speed by manipulation'of the hand :whejel' mechanism 54', at the same time the gas regulatingwalve ment'could be provided so that the operator couldiset the linkagerelationships so'that in operation'thegas pressure} being supplied to the engine would always exceed the scavenging air pressure'by a desired amount', andthe'" l. in a dual fuel. internal combustion engine-oflthe compression ignition typc,'ad apt'ed to operate under con f ditions of varying ioad and speed, the-engine havin'gla mechanism'associated with the avel-nearer varying the varying' the' amountuof oil fuel. being supplied {to the enginein accordance with the load during" the oiloperate -73 V 1 a a in}, range, manually operable means associated with the governor for varying the speed of the engine, and means for automatically varying the pressure of the gas sup plied to the engine as the rnanually operable means varies compression ignition type, adapted to operate under conditions of varying load and speed, the engine having a governor with a gas operating range and an oil operating range in the event-of a substantial gas pressure failure,

a blower for supplying scavenging air to the engine at a pressure that varies; with the speed of the engine, a gas supply line for supplying gas fuel to the engine from a gasifuel source, a pump for supplying oil fuel to the engine from an oil fuel source, a gas fuel control mechanism'associated .Withthe governor for varying the amount .j'Of' gas fuel beingsupplied to the engine in accordance with the loadfduring the 'gas operating range, an oil fuel control mechanism associated with the governor for varying the amount of oil:fuel being supplied to the engine in accordancewiththe load during the oil operatinglrange, manuallyloperable means associated with the governor for varying the speed" of the engine, and means for automatically varying the pressure of the gas suppliedto the engine as the manually operable means varies the speed, said last-mentioned means including a valve in the gas 7 1 supply line and'alinkage connected between it and'the manually. operable means so that as the speed of the engine is varied in'a manually selected manner, the pressure, of the gas being supplied .to' the engine. will also vary, the" gas fuel control mechanism, thevalve in the .j'gas'sup p'ly line,the manually operable speed varying means, andthe linkage being constructed and: arranged aiii V g 4. In a dual fuel internal combustion engine of the compression ignition type, adapted to operate under'cbn ditions of varying load and speed, the engine havinga cylinder, at piston'movably mounted in thecylinder, a

scavenging blower for the engine, a governor associated ewitht-th'e engine having a gas operating range and an oil op'era'ting range, means for supplying gas fuel to the. 7

cylinder; means for supplying; oil'fuel to the cylinder,

' means for 'varying the amount of fuel supplied to the cylinder in'accordance with the load, said last-mentioned SOLO)? the engine' and separate means for automatically varying thejpressure o f'the gas fuel supplied to the cylinf; der as the speed is varied by said last mentioned'means,

said last mentioned means being "constructed so ,thatgthe combustion-ignition:type adapted to operateunder condition s'jof varying-load and speed with a 'gas operating 1 range and an oiloperatin'g: ranlgythe engine having 'a cylinder, a' pisto n movably'mountedl in the Jcylinder, scavenginghlowenforthe engine; meansfor supplying V gas fuelto 'the cylinder during the gas operating "range in amounts that'yary in accordance with the IOadQmeans forsupplying oil fuel to the cylinderfduring the oil' ope'rajt ing range inamounts thatgvaryiin accordance'withthe;

load, and separate means for varying the pressure of the gas fuel supplied to the cylinder in accordance with the speed of the engine, said last mentioned means being constructed so that at all speeds the gas pressure Will always exceed the scavenging air pressure.

6. A method of operating a dual fuel internal combustion engine of the compression ignition type under conditions of varying load and speed, the engine having a gas operating range and an oil operating range, including the steps of varying the amount of gas fuel being supplied to the engine during the gas operating range in accordance with the load on the engine, varying the amount of oil fuel being supplied to the engine during the oil operating range in accordance with the load on the engine, and separately varying the pressure of the gas fuel being supplied to the engine automatically in accordance with the speed of the engine.

7. A method of operating a dual fuel internal combustion engine of the compression ignition type under conditions of varying load and speed, the engine being adapted to operate from a relatively constant pressure source of gas fuel and having a gas operating range and an oil operating range in the event of a substantial reduction in the pressure of the gas fuel from the relatively constant pressure source, including the steps of varying the amount of gas fuel being supplied to the engine during the gas operating range in accordance with the load on the engine, varying the amount of oil fuel being supplied to the engine during the oil operating range in accordance with the load on the engine when the pressure of the gas fuel from the relatively constant pressure source is substantially reduced, and separately varying the pressure of the gas fuel being supplied to the engine during the gas operating range automatically in accordance with the speed of the englue.

8. A method of operating a dual fuel internal combustion engine of the compression ignition type under conditions of varying load and speed, the engine having a gas operating range and an oil operating range, including the steps of supplying scavenging air to the engine at a pressure that varies at least with the speed, varying the amount of fuel oil supplied to the engine in accordance with the load during the oil operating range, varying the amount of fuel gas, with a quantity of pilot oil being supplied to the engine, in accordance With the load on the engine during the gas operating range, and automatically throttling the gas fuel supply so as to vary its pressure in accordance with the pressure of the scavenging air supplied to the engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,400,219 Barnaby et al. May 14, 1946 2,489,405 Doyle Nov. 29, 1949 2,509,960 Calhoun May 30, 1950 2,544,978 Blessing et al Mar. 13, 1951 

